TheRole of Biofilm and Sediment Accumulation and of Chlorine Tolerance inBacterial Regrowth

ReportNo WSAA 99

February 1996




Problemsof coliform non-compliance, which could not be linked to contamination events,were experienced in the Sydney drinking water distribution system during thelate 1970’s. Bacterial regrowth was subsequently found to be responsible for aproportion of the high coliform counts, with both Aeromonas hydrophila and klebsiellaoxytoca dominant in the regrowth within the system. The aim of this projectwas to determine the role of biofilm and sediment accumulation and of chlorinetolerance in the regrowth of these two organisms.


Analysisof flushing samples, collected from within Sydney’s drinking water distributionsystem, resulted in the isolation of total coliforms and A. hydrophila, but not K.oxytoca, from within any of the sampled zones. A significantly highernumber of total coliforms, A. hydrophilaand heterotrophic plate count bacteria were isolated from biofilms/sedimentswithin two of the four zones sampled. The absence of Klebsiella-type bacteria,in this sampling period, may have been the result of low winter temperatures orof a more effective control of these organisms by the management programadopted.


Resistanceof Kl. oxytoca to chlorine wasrelated to the formation of aggregates during growth. In addition, thesebacteria were able to recover after chlorine injury and grow on the organicmatter supplied by lysed cells.


Measuresfor the control of bacterial regrowth should include the removal of biofilms,sediments and cell aggregates before disinfection, as well as the reduction ofsediment and organic materials entering the system. Other control measuresshould include the maintenance of a chlorine residual throughout the system andthe implementation of routine flushing programs.


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